The Federal Bureau of Investigation (FBI) is the principal investigative arm of the United States Department of Justice (DOJ). Title 28, United States Code (U.S. Code), Section 533, which authorizes the Attorney General to "appoint officials to detect... crimes against the United States," and other federal statutes give the FBI the authority and responsibility to investigate specific crimes. At present, the FBI has investigative jurisdiction over violations of more than 200 categories of federal crimes[?]. The Ten Most Wanted List has been used since the 1930s to notify the public of wanted fugitives.

The mission of the FBI is to uphold the law through the investigation of violations of federal criminal law; to protect the United States from foreign intelligence and terrorist activities; to provide leadership and law enforcement assistance to federal, state, local, and international agencies; and to perform these responsibilities in a manner that is responsive to the needs of the public and is faithful to the United States Constitution.

"The FBI originated from a force of Special Agents created in 1908 by Attorney General Charles Bonaparte during the Presidency of Theodore Roosevelt...". At first it was named the Bureau of Investigation (BI) and it did not become the FBI until 1935.

Under J. Edgar Hoover, who became director of the FBI on May 10, 1924, the agency spent much of its energy on investigating political activists who were not accused of any crime (eg, Albert Einstein as a socialist). When Franklin Delano Roosevelt was president, Hoover had to be reminded that liberalism not only was not a crime, but was the politics of the incumbent president and his administration.

Hoover's investigation of Martin Luther King was also notorious--the FBI found no evidence of any crime, but attempted to use tapes of King involved in sexual activity for blackmail.

In the 1990s, it turned out that the FBI's crime lab had repeatedly done shoddy work. In some cases, the technicians, given evidence that actually cleared a suspect, reported instead that it proved the suspect guilty. Many cases had to be reopened when this pattern of errors was discovered.

As of June 2002, the FBI's official top priority is counter-terrorism. The USA PATRIOT Act granted the FBI increased powers, especially in wiretapping and monitoring of internet activity. One of the most controversial provisions of the act is the so-called "sneak and peek" provision, granting the FBI powers to search a house while the residents are away, and not requiring them to notify the residents for several weeks afterwards. Under the PATRIOT Act's provisions the FBI also resumed inquiring into the library records of those it suspected of terrorism, something it had supposedly not done since the 1970s.